I think the big reason that nobody’s mentioned yet is simply that they were earlier. Back when projects like Tox and Matrix were first starting to pop up, telegram was already fully formed. Signal didn’t come until at least a year later and didn’t have feature parity until several years later. Telegram by contrast was a much closer experience to WhatsApp and Messenger, making the transition much easier, particularly for low-tech knowledge users.
I think the big reason that nobody’s mentioned yet is simply that they were earlier. Back when projects like Tox and Matrix were first starting to pop up, telegram was already fully formed. Signal didn’t come until at least a year later and didn’t have feature parity until several years later. Telegram by contrast was a much closer experience to WhatsApp and Messenger, making the transition much easier, particularly for low-tech knowledge users.